Stands for supporting trees and other substantially cylindrical elements are known in the art and numerous examples show the complexity of the mechanisms used to clamp and support a substantially cylindrical element. The mechanisms are varied, but are typically inconvenient as they require the user to crouch, kneel or lie on the ground and tighten the clamps at the same time as the user holds the element in a vertical position. Often, a second user is required to hold the element in a substantially vertical position while the first user tightens the clamps.
Some known approaches use the weight of the element to create a clamping force that is present as long as the element is in the apparatus. For example, U.S. Pat. No. 2,464,593 (Lorenzen) describes a tree holder in which the weight of the tree rests on a spring-supported conical cup, or retaining member. The displacement of the cup due to the weight of the tree causes knife-edge gripping blades to pivotally engage the tree trunk. U.S. Pat. No. 3,301,512 (Nyberg) describes a stand in which the weight of the element on a retaining member causes movable clamping arms to pivot and engage the tree trunk. U.S. Pat. No. 4,007,901 (Mancini) also describes a tree stand in which the weight of the element in a central reservoir, or retaining member, causes the legs to pivot and engage clamping arms with the tree trunk. Finally, U.S. Pat. No. 6,661,519 (Cone) describes an apparatus in which clamping arms pivot to engage a tree in response to the weight of the tree placed in a centrally disposed reservoir or retaining member.
In the references noted above, each apparatus describes the clamping arms as pivoting towards the tree trunk. The '519 patent to Cone further describes a locking mechanism to lock the clamping arms to the tree trunk. Each clamping mechanism is prevented from disengaging the tree trunk by the force generated by the weight of the tree on the retaining member. The force is transmitted to the tree trunk through the clamping arms pivoting on a fulcrum and engaging with the tree trunk. For a given weight of an element, the force applied by a pivoting clamping arm on the element depends on the diameter of the element, with large diameter elements experiencing greater applied forces than smaller diameter elements. This non-constant application of force on the element is a function of the amount of displacement of the clamping arms, and can damage the substantially cylindrical element being held.
It is therefore desirable to provide an apparatus with improved force characteristics to hold a substantially cylindrical element.